I. Field
The present disclosure relates generally to electronics, and more specifically to power amplifiers (PAs).
II. Background
Power amplifiers are widely used in various wireless communication systems to provide amplification and output drive for radio frequency (RF) signals prior to transmission over the air. For example, power amplifiers are used in Global System for Mobile Communications (GSM) systems, Wideband Code Division Multiple Access (WCDMA) systems, etc. Power amplifiers are also used in base stations as well as in terminals.
Power amplifiers are typically required to meet various system specifications for spectral mask, transmit time mask, harmonics distortion, output noise, output power level, etc. GSM and WCDMA systems also require a terminal to be able to adjust its output power over a wide range, e.g., 30 dB or more for GSM, and more than 70 dB for WCDMA. In order to meet the various system specifications at the maximum output power level, power amplifiers are often designed with large-size transistors and biased with high current and/or voltage. The high bias current and/or voltage result in low efficiency for the power amplifiers at lower output power levels for the more common operating scenarios.
Many terminals are portable and powered by internal batteries. For a portable terminal, a power amplifier may consume a significant amount of battery power, which may then shorten both standby time between battery recharges and talk time during operation. Efficient power amplifiers with lower power consumption are thus highly desirable.